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Create RSpec matchers for negatable predicate methods

Problem

As noted in the documentation, there are cases where using not_to in an expect statement can be unintentionally inefficient because when the expect statement passes, the framework executes the positive predicate method (e.g., has_file?), waits 10 seconds for it to fail, then negates the result.

One solution to this problem is to use a negative predicate method instead (e.g., has_no_file?). For example expect(project).to have_no_file(name). The problem with this solution is that it is awkward phrasing, and we have to remember to write it that way rather than the more familiar option of using not_to.

Proposal

Create custom RSpec matchers for negatable predicate methods. For example, in gitlab-org/gitlab!46302 (merged) a negatable have_file matcher is defined:

  RSpec::Matchers.define :have_file do |file|
    match do |actual|
      expect(actual.has_file?(file)).to be true
    end

    match_when_negated do |actual|
      expect(actual.has_no_file?(file)).to be true
    end
  end

When it's used in a test, such as:

Page::Project::Show.perform do |project|
  expect(project).not_to have_file(file_name)
end

...instead of executing the page object's has_file? method, it uses the match_when_negated block to execute has_no_file?, and is therefore the same as expect(project).to have_no_file(file_name), but reads more naturally, and avoids the problem of having to use negative predicate methods when we're more familiar with using not_to.

Tasks

Edited by Sofia Vistas